Construction and use of low tension medical instrument

ABSTRACT

A method comprises providing a medical instrument having a first tendon that extends from an interface at a proximal end of the medical instrument to an actuated element at a distal end of the medical instrument. The first tendon has a first tension in the medical instrument as provided. The interface comprises a first plate connected to a second plate by a support. The first tendon has a portion extending between the first and second plate and passing through holes in the first and second plates. The interface also comprises an engagement structure attached to a proximal end of the first tendon. The method also comprises receiving the engagement structure into engagement with a manipulator which includes increasing tension in the first tendon from the first tension to a preload tension. After receiving the engagement structure, the actuated element is actuated by pulling the first tendon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent document is a divisional and claims benefit of the earlierfiling date of U.S. patent application Ser. No. 14/996,863, filed Jan.15, 2016, issued Feb. 6, 2018 as U.S. Pat. No. 9,883,915, which is adivisional and claims benefit of the earlier filing date of U.S. patentapplication Ser. No. 13/360,421, filed Jan. 27, 2012, issued Feb. 16,2016 as U.S. Pat. No. 9,259,277, which claims the priority of U.S.Provisional Pat. App. No. 61/485,697, filed May 13, 2011, all of whichare hereby incorporated by reference in their entirety.

BACKGROUND

Robotically controlled medical systems such as employed for minimallyinvasive medical procedures can include complex equipment to preciselycontrol and drive medical instruments. (As used herein, the terms“robot” or “robotically” and the like include teleoperation ortelerobotic aspects.) FIG. 1A illustrates an example of a knownrobotically controlled system 100. System 100, which may, for example,be part of a da Vinci® Surgical System available from IntuitiveSurgical, Inc., includes a patient-side manipulator 110 having multiplearms 130. Each arm 130 has a docking port 140 that generally includes adrive system with a mechanical interface for mounting and providingmechanical power for operation of an instrument 150. Arms 130 can beused during a medical procedure to move and position respective medicalinstruments 150 for the procedure.

FIG. 1B shows a bottom view of a known medical instrument 150.Instrument 150 generally includes a transmission or backend mechanism152, a main shaft 154 extending from the backend mechanism 152, and afunctional tip 156 at the distal end of main shaft 154. Tip 156generally includes a medical tool such as a scalpel, scissors, forceps,or a cauterizing instrument that can be used during a medical procedure.Drive members 155 such as cables or push-pull rods connect to tip 156and extend through main shaft 154 to backend mechanism 152. Backendmechanism 152 typically provides a mechanical coupling between drivemembers 155 of instrument 150 and motorized axes of the mechanicalinterface of docking port 140. In particular, backend mechanism 152typically contains mechanical elements such as capstans, gears, andlevers that convert rotational movement of drive motors into linearmotion of tendons or push rods 155.

Instruments 150 of system 100 can be interchanged by removing oneinstrument 150 from a docking port 140 and then installing anotherinstrument 150 in place of the instrument removed. Equipment such aspatient-side manipulator 110 is often covered for a medical procedure bya sterile barrier because of the difficulty in cleaning and sterilizingcomplex equipment between medical procedures. These sterile barriers caninclude a plastic sheet and a sterile adaptor (not shown) that isinterposed between docking port 140 and instrument backend 152. However,instruments 150 are on the patient side of the sterile barrier and aregenerally subject to surgical sterile protocols. The complexity ofbackend mechanism 152 can make sterilization of instruments 150difficult particularly if an instrument is intended to be reused formultiple medical procedures. The complexity of backend mechanism 152also increases the cost of instrument 150, which is particularly aconcern when an instrument is intended to be a single use device.

SUMMARY

In accordance with an aspect of the invention, a minimally invasivemedical system minimizes the complexity of the mechanical interfaceportion on the instrument. In particular, a manipulator that is outsidea sterile barrier can use a mechanical interface with nearly directaccess to connecting members such as cables or push-pull rods on thepatient side of the sterile barrier. For example, in some embodiments,only portions of the sterile barrier are between the manipulator and thetendon or push-pull rod that the manipulator actuates.

One specific embodiment of the invention is a system including a medicalinstrument having a main shaft, an actuated element connected to themain shaft, a drive member connected to the actuated element andextending through the main shaft; and a termination fixture at aproximal end of the main shaft. The drive member terminates at thetermination fixture, where the termination fixture provides an interfacethat exposes a portion of the drive member to direct access and movementby a system external to the medical instrument. In particular, theexternal system can include a manipulator system and a sterile barrier.

Another embodiment of the invention is a method for operating a medicalinstrument. The method includes installing a sterile barrier that is indirect contact with a drive member of the medical instrument. The drivemember may be a tendon, rod, or similar structure that extends through amain shaft of the instrument and connects to an actuated element of theinstrument. After the sterile barrier is installed, a manipulatoroperates or acts on the sterile barrier to transfer force through thesterile barrier to the drive member to thereby actuate the actuatedelement of the instrument.

Yet another embodiment of the invention is a method for constructing andusing a medical instrument. In particular, a medical instrument havingone or more tendons that extend from a proximal end of the instrument toan actuated element at a distal end of the instrument can be constructedwithout tension in the tendons or with tensions below those required fornormal operation of the instrument when in use attached to amanipulator. The construction process may thus be simplified,particularly because some manufacturing processes are made moredifficult by pre-tensioning of tendons. The instrument without tensionin the tendons can be used by first engaging the medical instrument witha manipulator to create tension in the tendons and then operating themanipulator to pull the tendons and actuate the medical instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a medical system that can employ removable instrumentswith mechanical interfaces in accordance with an embodiment of theinvention.

FIG. 1B shows a bottom view of a medical instrument having a backendmechanism that provides a known mechanical interface for actuation ofthe instrument.

FIGS. 2A and 2B illustrate operation of a portion of a medical system inwhich a mechanical interface of an instrument makes suspended portionsof tendons accessible to manipulators.

FIGS. 3A and 3B show portions of medical systems in accordance withembodiments of the invention respectively using cams and rack-and-pinionmanipulators for the tendons in a medical instrument.

FIG. 4 shows a portion of a medical system in accordance with anembodiment of the invention with manipulators that act on the sides ofsuspended portions of tendons and on proximal ends of the tendons.

FIG. 5 shows a side view of a medical system including an instrumenthaving a push-pull rod.

FIG. 6 shows a portion of a medical system in accordance with anembodiment of the invention including a medical instrument havingaccessible tendons in a cylindrical arrangement.

FIG. 7A shows a top view of a medical instrument having accessibletendons in a linear arrangement.

FIG. 7B shows a side view of the medical instrument of FIG. 7A andillustrates a manipulator operating on a tendon through an interveningsterile barrier.

FIG. 8 illustrates a portion of a medical instrument in accordance withan embodiment of the invention using rack and pinion drive at theproximal ends of connecting members.

FIG. 9 illustrates a portion of a medical instrument in accordance withan embodiment of the invention using friction drive at the proximal endsof connecting members.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION

In accordance with an aspect of the invention, a backend mechanism of amedical instrument can be simplified to reduce the amount of hardwarerequired in the medical instrument. In particular, the capital equipmentsuch as a patient-side manipulator (PSM) or other instrument manipulatorcan be adapted to act on extended drive members of the instrumentdirectly through a sterile barrier. The extended drive members, whichmay be tendons or push-pull rods, can be brought to a simple terminationfixture at the proximal end of the main shaft of the instrument. Thefixture and/or main shaft can then be plugged directly into a sterilebarrier and a port of a robotic control system. Mechanical elements suchas capstans, input dogs, levers, or other mechanisms conventionallyincluded in a backend of a medical instrument are not part of theinstrument and are not subject to surgical sterilization protocols.

FIG. 2A shows a proximal end of an instrument 200 having a main shaft210 through which tendons 221 and 222 extend. Main shaft 210 may be arigid tube, a flexible tube, or a set of linked vertebrae. Each tendon221 or 222 can be any type of flexible connecting member such as acable, a filament, a tube, or a rod that is able to support tensioncreated by pulling on the connecting member but is not required tosupport compression resulting from pushing on the connecting member. Theproximal ends of tendons 221 and 222 terminate at a fixture 230 that isattached to the proximal end of main shaft 210, and distal ends (notshown) of tendons 221 and 222 attach to one or more actuated mechanicalmembers or distal elements (not shown) of instrument 200. Such actuateddistal elements of robotically medical instruments are well known in theart and may be, for example, part of an end effector such as tip 156 ofFIG. 1B or may be an actuated vertebra that is part of main shaft 210.For illustration of the operation of an exemplary embodiment ofinstrument 200, tendons 221 and 222 are presumed to connect to the samedistal element of instrument 200 so that pulling on tendon 221 causesthe mechanical member to move or rotate in a first direction and pullingon tendon 222 causes the mechanical member to move or rotate in anopposite direction. In one commonly employed configuration of anarticulated element, pulling in a length of one tendon 221 or 222requires feeding out of an equal length of the other tendon 222 or 221,and tendons 221 and 222 may be opposite ends of a single cable thatwraps around a portion of the element. Many other configurations forarticulation of medical instruments are known and could be employed indifferent embodiments of instrument 200.

Tendons 221 and 222 exit the proximal end of main shaft 210 and passthrough holes or grooves in a plate 235 and a plate 233 of terminationfixture 230. Crimps, bends, beads, rings, or similar structures 231 and232 in or on tendons 221 and 222 can be used to limit movement of theproximal ends of tendons 221 and 222 in the distal direction and may beattached or affixed to plate 233 or may be free to be pulled in theproximal direction from plate 233. Plate 233 attaches to plate 235 andthe end of main shaft 210 through a support 234. Support 234 may berigid or may provide spring tension to plate 233 and attached tendons221 and 222 for a limited range of motion that is taken up wheninstrument 200 engages an instrument manipulator 260. Support 234provides a separation between plates 233 and 235, so that portions ofeach tendon 221 or 222 are suspended and accessible between plates 233and 235. The remaining portions of tendons 221 and 222 extend distallyfrom plate 235 through main shaft 210 to an actuated distal element ofinstrument 200.

Manipulators 241 and 242, which are part of PSM 260 outside a sterilebarrier 250, can act on the suspended portions of respective tendons 221and 222 that are exposed by fixture 230. In particular, a sidewaysdisplacement of a portion of a tendon 221 or 222 between plates 233 and235 applies tension and causes displacement of the distal end of thedisplaced tendon 221 or 222, since plate 233 and structures 231 and 232prevent the proximal ends of tendons 221 and 222 from moving in thedistal direction. Instrument 200 during a medical procedure will bewithin an area subject to surgical sterile protocols, while manipulators241 and 242 and the rest of the PSM will be outside sterile barrier 250.Instrument 200 has the advantage that sterile barrier 250 may be assimple as a plastic bag interposed between tendons 221 and 222 andmanipulators 241 and 242.

FIG. 2A shows a configuration of instrument 200 in which tendon 221 isstraight and manipulator 242 has pushed a portion of tendon 222 towardthe center axis of termination fixture 230. FIG. 2B illustrates movementof manipulator 241 that pushes a suspended section of tendon 221 towardthe center axis of termination fixture 230 and movement of manipulator242 that releases the deflection of tendon 222. Increasing thedeflection of tendon 221 pulls in the distal end of tendon 221, andreleasing the deflection of tendon 222 feeds a portion of tendon 222 outof the termination fixture 230 toward the distal end of instrument 200.Accordingly, movement of manipulators 221 and 222 can be used to actuatea distal element coupled to tendons 221 and 222.

FIGS. 2A and 2B shows an arrangement in which manipulators 241 and 242of PSM 260 can push on the sides of tendons 221 and 222 throughintervening sterile barrier 250 and deflect portions of tendons 221 and222 toward a center axis of main shaft 210. Alternatively, manipulators241 and 242 could be designed to pull or pluck respective tendons 221and 222 to cause deflections in any direction perpendicular to thelengths of tendons 221 and 222.

Manipulators 241 and 242 for tendons 221 and 222 may be implementedusing fingers, cams, or rollers, which contact respective tendons 221and 222. FIGS. 2A and 2B show an embodiment in which manipulators 241and 242 are fingers that contact tendons 221 and 222 and rotate about anoffset axis to push on tendons 221 and 222. Other methods for movingtendons are possible. FIG. 3A, for example, shows a portion of a medicalsystem in which manipulators 341A and 342A are cams that contact tendons221 and 222 and are shaped so that rotations of the cams deflect tendons221 and 222. FIG. 3B shows a portion of a medical system in whichmanipulators 341B and 342B are implemented using rack and pinion systemin which rack portions contact tendons 221 and 222 through sterilebarrier 250 and a pinion gear is coupled to a drive motor (not shown) sothat rotation of the pinion gear moves the rack and deflect tendons 221and 222. The manipulators, whether employing fingers, cams, or otherstructures to contact the tendons, may be actuated independently or maybe geared or coupled together within PSM 260, 360A, or 360B toaccomplish coordinated motion of two or more tendons if necessary toachieve smooth articulation of instrument 200. The gearing or couplingfor articulation of instrument 200 may be independent of a mechanismused to engage or disengage the manipulators and tendons duringinstallation or removal of instrument 200.

A process for installing instrument 200 in PSM 260 of FIG. 2A or 2B orPSM 360A or 360B of FIG. 3A or 3B needs to engage manipulators 241 and242, 341A and 341B, or 341B and 342 and respective tendons 221 and 222so that the PSM can control actuation of instrument 200. (The followingdescribes a process for installing instrument 200 in PSM 260 of FIG. 2Aor 2B. Similar processes may be used for installation in PSM inaccordance with other embodiments of the invention.)

Inserting the proximal end (e.g., termination fixture 230) of instrument200 into a matching port of PSM 260, e.g., port 140 of system 100 asshown in FIG. 1A, will generally bring tendons 221 and 222 into therange of motion of respective manipulators 241 and 242 but may not bringtendons 221 and 222 into contact with manipulators 241 and 242.Accordingly, PSM 260 will generally need to move manipulators 241 and242 into contact with tendons 221 and 222. In one embodiment, tendons221 and 222 in instrument 200 may initially have slack that isredistributed or removed as manipulators 241 and 242 move to fullyengage respective tendons 221 and 222. Alternatively, plate 233 or 235or tendons 221 and 222 may be spring loaded to provide pre-tension intendons 221 and 222 that may be less than the tension require for normaluse of instrument 200, and initially engaging instrument 200 withmanipulators 241 and 242 can involve pushing the spring or springs to alimit of its or their range of motion or locking the pre-tension systemso that the proximal ends of tendons 221 and 222 remain immobile duringoperation of instrument 200. However, instrument 200 withoutpre-tensioned tendons 221 and 222 may be easier to construct and lesssusceptible to thermal effects during high temperature sterilizationthan would a pre-tensioned instrument. A lack of tendon tension orreduced tendon tension in tendons 221 and 222 when instrument 200 is notengaged with manipulator 260 may provide for greater instrumentdurability when instrument 200 undergoes cleaning and sterilizationprocesses. In particular, a sterilization process in an autoclave orsimilar high temperature system differentially elongates tendons 221 and222 relative to main shaft 210 and other structures because ofdifferences in the coefficients of thermal expansion of the materialsthat may be used in different parts of instrument 200, and thedifferential expansion can stretch or damage tendons 221 and 222.Reduced tension in tendons 221 and 222 during reprocessing can reduce oreliminate damage that might otherwise occur in high temperaturesterilization processes. Also, a lack of tendon tension or reducedtendon tension in instrument 200 when instrument 200 is not engaged with260 manipulator may provide easier removal of instrument 200 whendisengaging instrument 200 from manipulator 260 during surgery.

Manipulators 241 and 242, during the installation process for instrument200, can simultaneously apply the same small initial force to removeslack from tendons 221 and 222 without actuating instrument 200. Thedeflections of tendons 221 and 222 when manipulators 241 and 242 applyconstant initial force will generally depend on how instrument 200 isposed, i.e., on the initial position of the distal element articulatedby tendons 221 and 222 and on the shape of main shaft 210 when mainshaft 210 is jointed or flexible. Thus, if there is no creep or stretchin tendons 221 and 222, the pose of instrument 200 may be inferred fromthe sideways displacements that the initial force during theinstallation process produces in tendons 221 and 222 and any otheractuating tendons (not shown) of instrument 200. This installationprocess can automatically compensate for cable creep or stretch over thelife of the instrument, but if tendons 221 and 222 have stretched by anunknown amount, an instrument control system for the PSM may establishthe initial position of instrument 200 using other techniques. Forexample, distal position sensing using a shape sensor or keeping thedistal portion of instrument 200 fixed in a rigid tube during engagementcould be used to establish the initial pose or instrument 200. Someexamples of shape sensors are described in U.S. Pat. App. Pub. No. US2007/0156019 A1 (filed Jul. 20, 2006), entitled “Robotic Surgery SystemIncluding Position Sensors Using Fiber Bragg Gratings” by Larkin et al.,and U.S. patent application Ser. No. 12/164,829 (filed Jun. 30, 2008)entitled “Fiber optic shape sensor” by Giuseppe M. Prisco, both of whichare incorporated herein by reference. Once manipulators 241 and 242engage tendons 221 and 222 further movements of manipulators 241 and 242can be used to articulate instrument 200.

Separate systems can be employed for tensioning an instrument duringinstallation and actuation of the instrument during operation. FIG. 4,for example, shows an instrument 400 that is used with a PSM 460 thathas two sets of manipulators. Manipulators 441 and 442 operate onsuspended portions of tendons 221 and 222, and manipulators 443 and 444operate on the proximal ends of tendons 221 and 222. The two sets ofmanipulators can be used for different purposes. For example,manipulators 441 and 442 may be used to engage or disengage tendons 221and 222 during installation or removal of instrument 400 at PSM 460, andmanipulators 443 and 444 may be used to pull on tendons 221 and 222 foractuation of instrument 400. Instrument 400 is similar to instrument 200of FIGS. 2A, 2B, 3A, and 3B and includes a main shaft 210 and tendons221 and 222 that may be as described above. Instrument 400 also includesa termination fixture 430 that includes plates 233 and 235 connected bya support 234 as described for fixture 230 above, but in fixture 430,tendons 221 and 222 are not affixed to plate 233. The proximal ends oftendons 221 and 222 in instrument 400 pass through holes in plate 233and terminate in end caps, beads, rings, crimps, or other structures 431and 432 that are shaped to be gripped and pulled. For example, endstructures 431 and 432 may be shaped to fit into respective forkedadapters 451 and 452, which may be fixtures of a sterile barrier 450,and manipulators 443 and 444 can be adapted to grip and pull on forks451 and 452. In one embodiment, adapters 451 and 452 are solidstructures that are fixed in a plastic sheet that is part of sterilebarrier 450, and slack or flexibility in sterile adapter 450 permitsmanipulators 443 and 444 to move adapters 451 and 452 (and endstructures 431 and 432 coupled to adapters 451 and 452) through a rangeof motion required for use of instrument 400.

During an exemplary process for installation of instrument 400,manipulators 443 and 444 grasp the respective end structures 431 and 432of tendons 221 and 222, e.g., through forked adapters 451 and 452 ofsterile barrier 450, then manipulators 441 and 442 advance to removeslack from respective tendons 221 and 222. Instrument 400 can then beactuated by the axial motion of end manipulators 443 and 444, while sidemanipulators 441 and 442 remain in their initial engaged positions.Alternatively, manipulators 443 and 444 can be used to remove slack, andmanipulators 441 and 442 can deflect tendons 221 and 222 for operationof instrument 400 as described above. To facilitate axial movement oftendons 221 and 222 during actuation of instrument 400, sterile barrier450 may include a resilient, low friction surface that contacts thesides of tendons 221 and 222. Again, a non-pre-tensioned instrument inan arbitrary pose may be engaged and actuated, if sufficient informationon the distal position of instrument 400 is separately available whenstretching or creep in tendons 221 and 222 are potential issues.

Instrument 400 can also be used with a PSM lacking side manipulators 441and 442. In that embodiment of the invention, the installation processfor instrument 400 includes end manipulators 443 and 444 moving to theirmost distal position, moving radially or sideways to engage endstructures 431 and 432, and then withdrawing proximally with low forceto remove the slack from each tendon 221 and 222. Since sidewaysdeflections of tendons 221 and 222 are not used, tendons 221 and 222 canbe replaced by push-pull rods or other rigid connecting members.Push-pull rods can employ rods, tubes, or other structures that aresufficiently rigid to support compression resulting from manipulators443 and 444 pushing on the ends of the push-pull rods. When manipulators443 and 444 engage push-pull rods, control processes that pull or pushon the push-pull rods may be employed for actuation of instrument 400.It may be noted that instruments employing push-pull rods can actuate amovable member through a single push-pull rod, so that complementarymovement of pairs of drive members are not required.

FIG. 5 shows a portion of an instrument 500 employing a push-pull rod520 that extends through a main shaft 210 from actuated element (notshown) at the distal end of push-pull rod 520 to an engagement structure531 at the proximal end of push-pull rod 520. As described above,push-pull rod 520 can be a rod, a tube, or any extended structurecapable of withstanding the tension and compression need for operationinstrument 500. A sterile barrier 550 separates medical instrument 500from a manipulator system 560. In the illustrated embodiment, sterilebarrier 500 includes an adapter 551 that may be fused into a portion ofa barrier sheet 552. A manipulator 540, e.g., a rack-and-pinion system540 connects to adaptor 551, which in turn connects to structure 530 onpush-pull rod 520. Manipulator 540 can move push-pull rod 520 by pushingor pulling on adaptor 551. In one embodiment of the invention, adaptor551 is solid structure fused into sheet 552 and relies on flexibility orslack in sheet 552 to accommodate the required range of motion ofpush-pull rod 520. Alternatively, adaptor 531 can be a multi-componentstructure including a slide that moves with push-pull rod 520 and aguide that remains fixed in sheet 552. In yet another alternativeembodiment, adaptor 551 may connect via a mechanical coupling tomanipulator 540 without breeching sterile barrier 550, thus simplifyingthe construction of sterile barrier sheet 552 by not requiring a fusedcomponent. This type of coupling between manipulator 540 and adaptor 551may rely on the flexibility and slack in sheet 552 to conform to theinterface between the 540 and 551 and to accommodate the required rangeof motion of push-pull rod 520.

Robotically controlled medical instruments generally require the use ofmany drive members for actuation of the medical instrument. Embodimentsof the invention can provide manipulator access to those drive membersusing a termination fixture with different geometry. FIG. 6, forexample, illustrates a portion of a medical system including aninstrument 600 having a termination fixture 630 that arranges tendons220 in a cylindrical formation for side access by manipulators 240,which can be implemented using a variety of mechanical systems includingbut not limited to those described above with reference to FIGS. 2A, 2B,3A, and 3B. For ease of illustration, a sterile barrier, which would beinterposed between a PSM 660 including manipulators 240 and instrument600, is not shown in FIG. 6.

FIG. 7A shows a top view of a portion of a medical instrument 700 inaccordance with an embodiment of the invention employing a lineararrangement of tendons 720. In instrument 700, tendons 720 are suspendedbetween walls 733 and 735 of a termination fixture 730 at the proximalend of a main shaft 710 of instrument 700. In particular, tendons 720have proximal ends that are prevented from moving in a distal directionat wall 733. Tendons 720 extend through and rest on holes or grooves inwall 735 and extend through main shaft 710 to actuate features (notshown) of instrument 700. Fixture 730 can be used to expand theseparation between tendons 720 (relative to the spacing within mainshaft 710) if more space between tendons 720 is desired in order toimprove manipulator access to tendons 720. In particular, the top offixture 730 can be open so that manipulators 740 in PSM 760 can accesstendons 720 as shown in FIG. 7B. FIG. 7B shows a sterile barrier 750that may be a plastic sheet interposed between manipulators 740 andtendons 720. Manipulators 740 in FIG. 7B employ a rack and pinionstructure allowing PSM 760 to control the amount of deflection of atendon 720 or sideways force applied to the tendon 720 by controllingthe movement or torque applied by a drive motor (not shown) for therack-and-pinion manipulator 740. Many other types of manipulators couldbe used to achieve the same movement of tendons 720.

FIG. 8 shows a portion of an instrument 800 having a mechanicalinterface exposing a drive member 820 (e.g., a tendon or push-pull rod)for actuation through a pinion gear 840 that may be part of amanipulator system 860 or part of a sterile barrier 850. FIG. 8 shows asingle drive member 820 but instrument 800 would typically containmultiple drive members for actuation of instrument 800, and drivemembers 820 may be arranged cylindrically as illustrated in FIG. 6,linearly as illustrated in FIG. 7A, or in any manner that presentsportions of drive members 820 for manipulation by a manipulator system860 outside of the sterile barrier 850 containing instrument 800. Ininstrument 800, each drive member 820 exits from the back of the mainshaft 810 as a rigid strut terminating in a gear rack 830 that may bepart of instrument 800 or alternatively part of an adapter in sterilebarrier 850. Gear racks 830 can have a fixed rotational orientation, oreach gear rack 830 may have teeth of a constant profile revolved aboutthe axis of the strut. Gear racks 830 are each engaged by respectivepinion gears 840 which may be at least part of an adaptor in sterilebarrier 850 or part of a manipulator on the PSM side of sterile barrier850. Idler rollers or gears 832 may be positioned to maintain thecorrect clearance between racks 830 and driving pinion gears 840. Theseidlers 732 or the axial position of each rack 830 may further be springloaded to minimize backlash between gear 840 and rack 830. Givenfeatures to align the major axis and the rotational position ofinstrument 800 with PSM 860 during instrument installation, each rack830 may be shaped to automatically engage its appropriate driving gear840 as instrument 800 is inserted axially (in a direction from distal toproximal) into PSM 860. If racks 830 are allowed to back-drive piniongears 840, PSM 860 may sense the initial position of each rack 830 byobserving when pinion gears 840 begins (or stops) turning, and thusdetermine final position when instrument 800 is seated in a port of PSM860. Further, if instrument 800 and PSM 860 are constructed such thatracks 830 are not back-driven by the insertion process, the distalinstrument pose of instrument 800 may be inferred from the initialpositions of racks 830. If the installation process includes PSM 860driving pinion gears 840 to apply and maintain a minimum preload on eachrack 830, instrument 800 may be retained in PSM 860 solely by thispre-tension and may later be released for disengagement by releasingthis pre-tension.

FIG. 9 shows an instrument 900 that may be operated in a manner similarto that of instrument 800 of FIG. 8, but instrument 900 uses a frictiondrive rather than a rack and pinion drive to move tendons or push-pullrods 820. The back end of each drive member 820 in instrument 900 maysimply include a section 930 having a surface on which a drive roller940 can ride. Section 930 may simply be the end portion of a rod orrigid tubing, flattened or otherwise, that is accessible to a driveroller 940 that is part of a sterile barrier 950 or part of PSM 960. Thedrive rollers 940 may be composed of high-friction materials, such asrubber, which may wear quickly. Accordingly, it may be advantageous toincorporate drive rollers 940 into a disposable sterile interfacecomponent that is part of sterile barrier 950 and is renewed or replacedfor each use of instrument 900. Unlike a rack and pinion drive, afriction drive may be allowed to slip under certain circumstances, whichmay be advantageous to the control scheme of the instrument. See, forexample, U.S. patent application Ser. No. 12/286,644, entitled “PassivePreload and Capstan Drive for Surgical Instruments,” which describesanother type of system that allows tendons to slip relative to themovement of a drive system.

Although the invention has been described with reference to particularembodiments, the description is only an example of the invention'sapplication and should not be taken as a limitation. Various adaptationsand combinations of features of the embodiments disclosed are within thescope of the invention as defined by the following claims.

What is claimed is:
 1. A method comprising: providing a medicalinstrument having a first tendon that extends from an interface at aproximal end of the medical instrument to an actuated element at adistal end of the medical instrument, wherein the first tendon has afirst tension in the medical instrument as provided, and wherein theinterface comprises: a first plate connected to a second plate by asupport, the first tendon having a portion extending between the firstand second plate and passing through holes in the first and secondplates; and an engagement structure attached to a proximal end of thefirst tendon; receiving the engagement structure into engagement with amanipulator that is configured to actuate the actuated element, whereinreceiving the engagement structure includes increasing tension in thefirst tendon from the first tension to a preload tension; and afterreceiving the engagement structure, actuating the actuated element bypulling the first tendon.
 2. The method of claim 1, wherein receivingthe engagement structure comprises: contacting the first tendon with afirst portion of the manipulator; and moving the first portion of themanipulator until the first tendon has the preload tension.
 3. Themethod of claim 2, wherein actuating the actuated element comprisesusing a second portion of the manipulator to pull the first tendon. 4.The method of claim 3, wherein the first portion of the manipulatorcontacts a suspended portion of the first tendon at a location away froman end of the first tendon and the second portion of the manipulatorcontacts the end of the first tendon.
 5. The method of claim 2, whereincontacting the first tendon comprises the manipulator contacting thefirst tendon via an intervening sterile barrier.
 6. The method of claim1, wherein receiving the engagement structure comprises applying aninitial force to the first tendon to remove slack from the first tendonwithout actuating the actuated element.
 7. The method of claim 1,wherein the first tension is zero and the first tendon has slack that isremoved when receiving the engagement structure.
 8. The method of claim1, further comprising determining an initial pose of the medicalinstrument when the first tendon has the preload tension.
 9. The methodof claim 1, wherein the medical instrument further includes a secondtendon that extends from the interface to the actuated element, thesecond tendon having a second tension in the medical instrument asprovided.
 10. The method of claim 9, wherein receiving the engagementstructure further includes increasing tension in the second tendon fromthe second tension to the preload tension.
 11. The method of claim 9,wherein: pulling the first tendon moves the actuated element in a firstdirection along a degree of freedom of the actuated element; pulling thesecond tendon moves the actuated element in a second direction along thedegree of freedom of the actuated element, the second direction beingopposite the first direction; the manipulator maintains the preloadtension in the second tendon while pulling the first tendon; and themanipulator maintains the preload tension in the first tendon whilepulling the second tendon.
 12. The method of claim 1, wherein providingthe medical instrument comprises constructing the medical instrument sothat the first tendon has the first tension as constructed, the firsttension being less than the preload tension.
 13. A medical instrumentcomprising: an actuated element at a distal end of the medicalinstrument; an interface at a proximal end of the medical instrument;and a first tendon that extends from the actuated element into theinterface, wherein the first tendon has a first tension in the medicalinstrument when the medical instrument is disengaged from a manipulator,wherein the interface comprises: a first interface portion configured toengage with the manipulator, wherein the manipulator employs the firstinterface portion to increase tension in the first tendon from the firsttension to a preload tension; and a second interface portion configuredto engage the manipulator, wherein the manipulator employs the secondinterface portion to pull the first tendon and thereby actuate theactuated element; wherein one of the first interface portion and thesecond interface portion includes a first plate connected to a secondplate, wherein a portion of the first tendon extends between the firstand second plates and passes through holes in the first and secondplates, and wherein another of the first interface portion and thesecond interface portion includes an engagement structure attached to aproximal end of the first tendon, the engagement structure being shapedto engage with the manipulator.
 14. The medical instrument of claim 13,wherein the manipulator is configured to contact the first tendon with afirst portion of the manipulator and to move the first portion of themanipulator until the first tendon has the preload tension.
 15. Themedical instrument of claim 13, further comprising a sterile barrierdisposed between the manipulator and the portion of the first tendonextending between the first and second plates.
 16. The medicalinstrument of claim 13, wherein the manipulator is configured to engagethe first interface portion to apply an initial force to the firsttendon to remove slack from the first tendon without actuating theactuated element.
 17. The medical instrument of claim 16, wherein thefirst tension is substantially zero.
 18. The medical instrument of claim13, further comprising: a second tendon that extends from the actuatedelement into the interface, the second tendon having a second tension inthe medical instrument when the medical instrument is disengaged from amanipulator.
 19. The medical instrument of claim 18, wherein themanipulator is configured to contact the second tendon with a portion ofthe manipulator and to move the portion of the manipulator until thesecond tendon has the preload tension.
 20. The medical instrument ofclaim 19, wherein: the manipulator is configured to maintain the preloadtension in the second tendon when the first tendon is pulled; and themanipulator is configured to maintain the preload tension in the firsttendon when the second tendon is pulled.